It is 15 years since the 9/11 terror attacks shook the world. Four co-ordinated terrorist attacks by al Qaida on the US killed nearly 3,000 people.
Two planes crashed into the World Trade Centre in New York. The 110 storey towers collapsed within an hour and 42 minutes.
A third plane crashed into the Pentagon in Virginia. The fourth crashed in a field after its passengers tried to thwart the attack.
The United States responded to the attacks by launching the war on terror. They invaded Afghanistan and killed Osama Bin Laden, al Qaida’s founder, in 2011.
On every anniversary, the names of the victims are read out at Ground Zero.
People have taken to Twitter under the hashtag #NeverForget to pay tribute to those who lost their lives 15 years ago.
Doesn't matter how many years go by #NeverForget r.i.p👼🏻— Jax (@jaxonmiller8) September 11, 2016
A day that shook the world. A day we will #NeverForget— Thomas Parker (@TomParker) September 11, 2016